Numerous polyurethane adhesive systems are known for adhering polyvinyl chloride but most are deficient in some respect such as poor hot peel properties, poor bond strength, and poor solubility in conventional adhesive solvents.
Several polyester-based polyurethane adhesives are commercially available for bonding plasticized polyvinyl chloride but these are generally deficient in their hot peel properties.
Polyether-based polyurethanes have also been suggested for adhesive applications. U.S. Pat. No. 2,929,800 to Hill broadly discloses as useful in adhesive compositions a polyurethane prepared from a polyalkyleneether glycol, a molar excess of an organic diisocyanate and a chain-extending agent. However, some of the polyurethane compositions taught in the patent are deficient as adhesives in certain respects, as, for example, hot peel, bond strength, and solubility in conventional solvents such as methyl ethyl ketone.
U.S. Pat. No. 2,899,411 to Schollenberger discloses polyurethane compositions prepared from poly(polymethylene oxide), a saturated aliphatic glycol and a diphenyl diisocyanate. Such polyurethanes, not being soluble in conventional adhesive solvents such as methyl ethyl ketone, usually result in poor adhesive systems. In general, adhesives prepared from compositions disclosed in the patent also have high heat activation temperatures, rendering them undesirable for use with plasticized polyvinyl chloride.
There is, therefore, a need for a polyurethane composition which is useful in adhesive applications, which is soluble in conventional solvents such as methyl ethyl ketone, and which results in adhesive systems exhibiting good hot peel properties, good bond strength, and desirable heat-activation temperatures for use with plasticized polyvinyl chloride.